Design and Simulation of Accelerating Structures for Future Linear Colliders

In order to obtain high luminosity and energy efficiency in future linear colliders, it is desirable to accelerate a train of closely spaced bunches on each rf pulse of the machine. There can be severe multibunch beam break-up in such a collider unless some means of strongly suppressing the transverse wakefield is incorporated into the design of the accelerating structures. Two methods of wakefield suppression will be discussed in this paper: (1) damping, i.e., lowering the external Q’s of the unwanted higher-order modes induced by the beam in the cells of the accelerating structures, and (2) detuning, i.e., varying the frequencies of the higher-order modes (by varying the cell and iris radii along the structure) so that the net induced wakefield rapidly decoheres. The design and simulation of damped and detuned structures will be discussed. Beam dynamics simulations incorporating an accelerating structure design for the SLAC Next Linear Colider (NLC) are presented.